WO 2006/063552 A1 relates to a motor vehicle headlamp element having at least one light emitting diode (LED) and at least one control facility which is suitable for processing a signal dependent on a measured value and to inject a current in accordance with the signal into the light emitting diode, wherein the control facility and the light emitting diode are arranged on a common carrier.
US 2004/0036418 A1 relates to a circuit and to a method for providing a closed control circuit using continuous current switching techniques. By means of controlling the current which is supplied to the light emitting diodes (LEDs), the LEDs are able to be operated with or close to their maximum capacity without the danger of overloading the LEDs or of disproportionate amounts of current being used. A circuit has a number of high-side switches of which each is connected to an LED array. The LED arrays are connected via a coil to a current switching operating point which switches current to ground or feeds the current back again in order to maintain an LED current flow in a desired area.
US 2006/0006821 A1 relates to a system and method for implementing an LED-based lamp which contains one or more color channels. The lamp comprises a controller which uses optical scanning and feedback to control LEDs in each channel so that they provide a full-range luminous intensity and/or color output. The optical feedback loop is designed to provide the light controller with an even luminous intensity and/or color of the light output. The controller is then designed to set a current and/or a pulse width modulation (PWM) duty cycle which will be fed to separate color channels of the lamp in order to obtain the desired luminous intensity and/or color.
US 2002/0097000 A1 relates to an LED lighting system to provide power for LED light sources in order to provide a desired light color, which has a power supply stage which is designed to provide a direct current signal. A light mixing circuit is coupled to the power supply stage and comprises a plurality of LED light sources with red, green and blue color, in order to generate light with different desired color temperatures. A control system is coupled to the power supply stage and is designed provide control signals to the power supply stage in order to hold the direct current signal at a desired level in order to maintain the desired light output. The control system is further designed to estimate associated lumen output components for the LED light sources and to do this is based on a transition temperature of the LED light sources and chromaticity coordinates of the desired light to be generated at the light mixing circuit. The light mixing circuit also has a temperature sensor for measuring the temperature associated with the LED light sources and a light detector for measuring a lumen output level of light generated by the LED light sources. Based on the measured temperatures the control system determines the quantity of output lumens that each of the LED light sources must generate in order to achieve the desired mixed light output, and the light detector in conjunction with a feedback loop maintains the required lumen output for each of the LED light sources.
DE 10 2005 049 579 A1 relates to a light source which radiates mixed-color light containing light of at least two different colors, which is radiated by a plurality of primary light sources in which the primary light sources are divided up into groups and the brightness values of the primary light sources within a group are determined and controlled separately according to color, so that the color location of the mixed-color light lies in a predetermined range of the standard color table. Furthermore a method for controlling such a light source is specified as well as a lighting device with such a light source, for backlighting a display for example.